Partially free, partially a purchase:
I took advantage of a first pair free promotion on coastal.com that I learned about on slickdeals. I had to upgrade the lenses because of my prescription, so I ended up paying around $50 (if my prescription was lower, everything but around $10 for shipping would have been free). I could have gone with $40 lenses, but I figured for the extra $10, I may as well get the thinnest/best lenses available.
Oh, the lens upgrade also includes free 3 day FedEx shipping.